This invention discloses an optical and computation system that does not utilize moving parts, which enables the angular orientation of the optical axes on the surface of a birefringent material to be determined and comparably, the orientation of the optical axes within light emerging from that surface. Further, since this invention considers the relative orientations of the preferred axis or axes of polarization within light, this method is also applicable for determining the angular orientation of the preferred axis of polarization of elliptically or linearly polarized light or the orientation of the polarizing axis of the material causing the preferred direction of polarization. For birefringent generated axes, this invention allows for the principal axis to be identified distinctly from the quadrature axis and without ambiguity. This is achieved by consideration of the relative intensities of the light emerging from the birefringent or polarizing material when observed through a plurality of linear or elliptical polarizers whose axes are set at known and distinct orientations to the reference direction of the measurement system, and with the ambiguities in the determination of the principal axis in the birefringent system removed by use of the phase of the interference patterns resulting when the light passing along the principal and quadrature axes within the birefringent material is combined by the linear or elliptical polarizers.
Classically when the axial directions of birefringent material have been considered, it has been in the context of photo-elastic measurement techniques. These generally utilize a combination of observations using linear polarized light to identify regions of similar optical axial directions, isoclinics, superimposed on fringes of comparable optical retardation, isochromatics; and the subsequent use of circular polarized light to separate the isoclinics from the isochromatics: procedures requiring operator intervention and decision making and further, requiring changes to the equipment and use of rotating linear polarizers to measure the axial directions. There have been several approaches to overcoming the need for operator intervention and decisions, which have recognised that if the emerging light is scanned in a circular fashion with a linear or near linear elliptical polarizer, the intensity of the light varies sinusoidally as a function of rotation angle, with four complete cycles discernable in the case of birefringence and two cycles for linear or elliptical polarization for each 2.pi. of rotation; consideration of the angular locations of the intensity maxima and minima then establishes the angular location of the optical axes. However this approach does not separately identify the principal axis within the birefringent material, being that aligned to the optical axis in the material along which light passes faster than along the axis in quadrature.